LNG Delivery System With Saturated Fuel Reserve

ABSTRACT

A cryogenic fluid delivery system includes a main tank system with a main tank adapted to contain a first supply of cryogenic liquid, and reserve tank system with reserve tank adapted to contain a second supply of cryogenic liquid. A pressure building circuit is adapted to delivery vapor to the head space of the main tank to build pressure in the main tank and a fuel delivery line supplies cryogenic fuel from either the main tank or the reserve tank to a use device. The reserve tank stores saturated cryogenic fuel that is delivered to the use device via the fuel delivery line while the cryogenic liquid in the main tank is being saturated. The fluid delivery system automatically switches to delivering cryogenic fuel from the main tank to the use device via the fuel delivery line upon saturation of the cryogenic liquid in the main tank.

REFERENCE TO PRIORITY DOCUMENT

This application claims priority to co-pending U.S. Provisional PatentApplication Ser. No. 62/004,477 entitled “LNG Delivery System withSaturated Fuel Reserve”, filed May 29, 2014. Priority to theaforementioned filing date is claimed and the provisional application isincorporated herein by reference in its entirety.

BACKGROUND

This disclosure relates to a system for delivering liquefied natural gas(LNG) from a storage tank to a use device, such as a natural gas poweredvehicle engine. The disclosed devices and methods can be used in avariety of environments and are particularly suited for markets in whichpre-saturation of the LNG fuel is not performed. The disclosed devicesand methods may be used as a source of “trim heat” if the storage tankpressure falls below a pre-defined level.

Many heavy-duty, natural gas fueled vehicle engines require that anintake pressure of natural gas be at a certain value, such as around 100psig. In most markets, LNG is saturated, or heat is added, to a point atwhich its vapor pressure is roughly equal to the pressure required bythe use device (i.e., the vehicle). This process of building saturationpressure is typically performed at LNG fueling stations. However, thereexist some markets in which this saturation of the fuel beforetransferring it to the vehicle storage tank is not performed or is notperformed to an extent great enough to achieve 100 psig saturated liquidin the vehicle tank after fueling. Thus, the storage tank may end upbeing filled with LNG well below the desired pressure. Additionally,some engines require pressures around 150 psig, which is not readilyavailable, even at fuel stations that saturate the fuel before delivery.

In one proposed solution, compressed natural gas (CNG) is used to addvapor pressure above LNG to deliver the fuel at an elevated pressure.However, this solution requires a second tank for CNG be mounted on thevehicle, which adds weight and occupies valuable space on the vehiclechassis. In another proposed solution, a specialized fuel stationsequentially fills the storage tank with LNG then uses natural gas vaporto add additional heat to saturate the fuel in the storage tank. Thevehicle fuel system is equipped with a special overflow tank into whichexcess LNG passes during the fill. However, this solution requires aspecial fuel station where the vehicle must be filled.

Another proposed solution utilizes an overflow tank, but also usesspecial main tanks that remain hydraulically full to maintain sufficientpressure to the engine no matter the liquid's saturation pressure.However, the special fuel tanks add extra cost and complexity to thesystem.

SUMMARY

Disclosed is an LNG delivery system that overcomes the aforementionedshortcomings of the prior art. In an embodiment the system uses a systemof one or more main tanks along with a reserve tank wherein the tankscan be mounted on a movable vehicle. The main tanks may utilize apressure building circuit of the type sometimes used on stationarycryogenic cylinders. This type of pressure building circuit utilizes agravity to feed liquid cryogen into a vaporizer. Upon vaporization ofthe liquid, its volume expands and the evolved gas is routed to a vaporspace above the cryogen in the main tank, building a head of vaporpressure above the liquid phase in the tank. Alternatively, gas fromdownstream in the fuel system (after the heat exchanger) can be pushedback to the vapor space by means of mechanical action. U.S. patentapplication Ser. No. 14/044,622 describes a related device and methodfor such a mechanical pressure building action and is incorporatedherein by reference.

Neither the traditional-style pressure building circuit nor themechanical action pressure builder on a vehicle storage tank can alonemaintain a constant supply of pressurized LNG. Since LNG vehicle tanksare used in mobile applications, any vapor pressure that is built abovethe liquid phase will quickly collapse as soon as the vehicle is inmotion and the liquid and vapor phases mix. It may take an inconvenientamount of time, such as an hour, to add enough heat in this fashion tofully saturate the bulk of LNG in the tank.

Therefore, in addition to a tank using a form of pressure-building, areserve tank is used in the system that stores saturated liquid that thevehicle can use to drive while the main tank(s) are being saturated.Once the liquid in the main tanks is saturated, the main tank(s) fuelthe vehicle with their now-saturated liquid and refill the reserve tank,which will be stored until next fill.

In one aspect, there is disclosed a cryogenic fluid delivery systemcomprising: a main tank system, the main tank system including a maintank adapted to contain a first supply of cryogenic liquid, the maintank including a head space adapted to contain a vapor above cryogenicliquid stored in the main tank; a reserve tank system, the reserve tanksystem including a reserve tank adapted to contain a second supply ofcryogenic liquid, the reserve tank including a head space adapted tocontain a vapor above cryogenic liquid stored in the reserve tank; apressure building circuit adapted to delivery vapor to the head space ofthe main tank to build pressure in the main tank; a fuel delivery linethat supplies cryogenic fuel from either the main tank or the reservetank to a use device; wherein the reserve tank stores saturatedcryogenic fuel that is delivered to the use device via the fuel deliveryline while the cryogenic liquid in the main tank is being saturated, andwherein the fluid delivery system switches to delivering cryogenic fuelfrom the main tank to the use device via the fuel delivery line uponsaturation of the cryogenic liquid in the main tank

Other features and advantages should be apparent from the followingdescription of various embodiments, which illustrate, by way of example,the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a prior fuel delivery system.

FIG. 2 shows an example embodiment of a fuel delivery system with areserve tank and a main tank.

FIG. 3 shows another embodiment of the fuel delivery system with a maintank using a traditional style pressure building loop.

DETAILED DESCRIPTION

Before the present subject matter is further described, it is to beunderstood that this subject matter described herein is not limited toparticular embodiments described, as such may of course vary. It is alsoto be understood that the terminology used herein is for the purpose ofdescribing a particular embodiment or embodiments only, and is notintended to be limiting. Unless defined otherwise, all technical termsused herein have the same meaning as commonly understood by one skilledin the art to which this subject matter belongs.

FIG. 1 shows an example of a fuel delivery system such as the typedescribed in U.S. patent application Ser. No. 14/044,622, which isincorporated herein by reference. A cryogenic tank 22 contains cryogenicproduct, such as LNG, that includes liquid cryogen 26 with vapor space36 above the liquid cryogen. A liquid line 24 communicates with thebottom region of the tank 22 where the liquid 26 is contained. As usedherein, a “line” can be any type of tubing or piping through which fluidcan flow. A product withdrawal line 28 connects the liquid line 24 tothe gas use device such as a vehicle engine. A heat exchanger orvaporizer 32 is located in a withdrawal line 28 to vaporize the cryogenbefore it is delivered to the use device. A valve 10 in the withdrawalline 28 represents, for example, an automatic valve.

With reference still to FIG. 1, an economizer circuit 34 includes avapor line or tube 40, which communicates with the vapor space 36. Thevapor tube 40 includes an economizer regulator 38, which is set at apredetermined pressure threshold. A liquid line 24 communicates withliquid 26 in the tank 22. When the pressure in tank 22 exceeds thepressure set point of regulator 38, vapor 36 may be withdrawn throughthe vapor line 40 and to the use device through the withdrawal line 28.This results in a lowering of the pressure in the tank 22. Due to thehorizontal nature of LNG vehicle fuel tanks, there is often sufficienthydrostatic pressure to cause liquid 26 to be withdrawn even when theregulator 38 is open. Therefore, a biasing relief valve 42 is includedin the liquid line 24 to cause the economizer circuit 34 to be the pathof least resistance out of the tank 22 when the regulator 38 is open. Asmall orifice 44 is located in parallel with relief valve 42 to allowback flow to the tank during transient periods of high to low use.

As shown in FIG. 1, an active pressure building circuit 55 can be usedto build head pressure in tank 22. The pressure building circuit 55includes an inlet line 51, which branches off withdrawal line 28downstream of the vaporizer 32. A flow inducer 52 causes vaporized gasto flow from the inlet line 51 to an outlet line 53 leading back to thetank 22. The outlet line 53 returns the gas to the vapor line 40 througha check valve 54.

FIG. 2 shows an example embodiment of a fuel delivery system with areserve tank 62 and a main tank 22. The tank 22 and 62 may beconstructed, for example, of a single outer vessel with one or moreinsulated inner vessels. A vacuum space is located between the vesselswithin the outer vessel. Other configurations of the tanks 22 and 62 arepossible.

In the embodiment of FIG. 2, the system includes a pressure buildingcircuit 55 as described with respect to FIG. 1. The reserve tank 62includes all of the same components as tank 22 (described above withreference to FIG. 1) and connects to the use device in parallel via afuel line 75. For example, the reserve tank 62 includes liquid 66 andthe vapor space 76 located above the liquid 66.

The reserve tank 62 includes an economizer circuit 44 a vapor line ortube 80, which communicates with the vapor space 76. The vapor tube 80includes an economizer regulator 78, which is set at a predeterminedpressure threshold. A liquid line 64 communicates with liquid 66 in thetank 62. When the pressure in tank 62 exceeds the set point of regulator78, the vapor 76 may be withdrawn through the vapor line 70 and to theuse device through the fuel line 75. This results in a lowering of thepressure in the tank 62. A biasing relief valve 82 is included in theliquid line 64 to cause the economizer circuit 74 to automatically bethe path of least resistance out of the tank 62 when the regulator 78 isopen. A small orifice 84 is located in parallel with the relief valve 72to allow back flow to the tank during transient periods of high to lowuse

With reference still to FIG. 2, a line 73 is the fill line for the tank62 and tees into the withdrawal line 28. A check valve 71 in the line 73prevents flow back from tank 62 into the main tank 22 system.

FIG. 3 shows another embodiment of the fuel delivery system with a maintank 22 and a reserve tank 62 as described above with reference to FIG.2. The system of FIG. 3 includes a traditional style pressure-buildingloop or circuit 27, which is used to build pressure within the main tank22. In this embodiment, a withdrawal line 23 extends downwardly from theliquid 26 in the tank 22. The withdrawal line 23 includes a vaporizer25. The liquid 26 exits the withdrawal line 23 via a gravity feed. Theexiting liquid 26 passes through the vaporizer 25, where it is changedto a vapor, and returns to the vapor space 36 through a check valve 54.In this manner, the pressure building circuit 27 increases pressurewithin the main tank 22.

In use, the reserve tank(s) retain a supply of previously saturatedliquid. When the use device is filled, only the main tank(s) is filledwith cold liquid. The reserve tank contains enough fuel to drive the usevehicle until the main tank becomes saturated. Pursuant to one method,the reserve tank is maintained in a normally empty state such that thereserve tank is empty upon arrival to the fuel station. Upon arrival ata fuel station, the liquid in the main tank is manually emptied into thereserve tank. The main tank is then filled with cold liquid at the fuelstation. The use device uses fuel from the reserve tank while the maintank is saturated. When the reserve tank is nearly empty, the systemswitches to using fuel from the main tank for the use device. The usedevice can then operate until the main tank is nearly empty.

In an alternate process, the reserve tank is maintained in a normallyfull state such that the reserve tank is full of liquid upon arrival toa fuel station. The main tank is then filled with cold liquid fuelstation. The main tank is saturated while the use device uses fuel fromthe reserve tank. When the reserve tank is nearly empty, the use deviceswitches to using fuel from the main tank. As the main tank becomesfully saturated, the reserve tank refills with liquid from the maintank. When the reserve tank is full, the feeling of the reserve tank isstopped and the use device continues while only using fuel from maintank. This device can then drive until the main tank is nearly empty.

An example setup and operation of the described system for fueling anengine is now described using numerical values as non-limiting examples.In an example embodiment, the system for fueling an engine needs 10 barginlet pressure. The economizer 38 has a set pressure of 12 barg and theeconomizer 78 has a set pressure of 11 barg. When the truck arrives atthe fuel station, the reserve tank is −90% full of liquid saturated at11 barg and the main tanks are nearly empty, but the liquid that remainsis saturated at 11 barg. The main tanks are filled with cold liquidsaturated at, for example, 4 barg. After the fill, all tanks are full;the main tank is full of liquid saturated at just above 4 barg, and thereserve tank is full of liquid saturated at 11 barg. The valve 10 is ina closed state and the valve 50 is in an open state.

Continuing the example, the truck can operate using the liquid in thereserve tank 62 for the first 30 minutes or 1 hour of driving. Duringthis time, the pressure building system 55 or 27 is acting on the maintank alone to build pressure and saturate the liquid in the main tank to11 barg. By the time the reserve tank 62 is nearly empty, the main tankhas sufficient pressure to be able to provide a constant source of highpressure to the engine. The control valve 10 will then open and thevalve 50 will close. Then the pressure building system will buildpressure up to 12 barg. When the liquid level in the main tank 22 fallsto a predetermined threshold (such as, for example 60-70%), then thevalve 50 will open and the valve 10 will close. This causes the reservetank 62 to refill from the main tank 22 while providing high pressuregas to the engine. When the reserve tank 62 is full, the valve 50 willclose and the valve 10 will open and the pressure building system willonly maintain 11 barg. Then the vehicle will drive for the remainder ofthe fuel in the main tanks.

In an embodiment, further control can be provided to keep the reservetank pressure down while driving by strategically switching to use thereserve tank and also keep it filled to a desired level. In thisembodiment, the system includes a control system that takes inputs onthe fill levels and pressure levels of each of the main tank 22 and thereserve tank 62. Additionally, to provide further control, the pressurebuilding system of the main tank can strategically build pressure todifferent amounts depending on the level in the reserve tank. Forexample, immediately after fueling, it is undesirable for the main tankto build pressure greater than that of the reserve tank because then thereserve tank can begin to fill with perhaps cold liquid. Instead, it isdesirable for the main tank to only build pressure to just less than thereserve tank until the reserve tank is nearly empty. Thereafter, itbuilds pressure to a higher setpoint and later fill the reserve tank asmentioned above with primarily saturated liquid. This level of controlis easily attainable with standard pressure sensors, level sensors andsolenoid valves known in the art.

In any of the embodiments, multiple main tanks can be connected inparallel, sharing a fill connection, sharing return gas line 53, andsharing withdrawal line 28.

Although embodiments of various methods and devices are described hereinin detail with reference to certain versions, it should be appreciatedthat other versions, embodiments, methods of use, and combinationsthereof are also possible. Therefore the spirit and scope of theappended claims should not be limited to the description of theembodiments contained herein.

1. A cryogenic fluid delivery system comprising: a main tank system, themain tank system including a main tank adapted to contain a first supplyof cryogenic liquid, the main tank including a head space adapted tocontain a vapor above cryogenic liquid stored in the main tank; areserve tank system, the reserve tank system including a reserve tankadapted to contain a second supply of cryogenic liquid, the reserve tankincluding a head space adapted to contain a vapor above cryogenic liquidstored in the reserve tank; a pressure building circuit adapted todeliver vapor to the head space of the main tank to build pressure inthe main tank; a fuel delivery line that supplies cryogenic fuel fromeither the main tank or the reserve tank to a use device; wherein thereserve tank stores saturated cryogenic fuel that is delivered to theuse device via the fuel delivery line while the cryogenic liquid in themain tank is being saturated, and wherein the fluid delivery systemswitches to delivering cryogenic fuel from the main tank to the usedevice via the fuel delivery line upon saturation of the cryogenicliquid in the main tank.
 2. A system as in claim 1, wherein the maintank system further comprises: a main liquid withdrawal line adapted tocommunicate with cryogenic liquid stored in the main tank and to deliverthe cryogenic liquid to a delivery line that communicates with a usedevice; a main economizer circuit in communication with the main liquidwithdrawal line and the head space of the main tank, the main economizercircuit adapted to direct vapor from the head space to the main liquidwithdrawal line when a pressure in the main tank rises above apredetermined maximum pressure;
 3. A system as in claim 1, wherein thereserve tank system further comprises: a reserve tank adapted to containa second supply of cryogenic liquid, the reserve tank including a headspace adapted to contain a vapor above cryogenic liquid stored in thereserve tank; a reserve liquid withdrawal line adapted to communicatewith cryogenic liquid stored in the reserve tank and to deliver thecryogenic liquid to a delivery line that communicates with a use device;a reserve economizer circuit in communication with the reserve liquidwithdrawal line and the head space of the reserve tank, the reserveeconomizer circuit adapted to direct vapor from the head space to thereserve liquid withdrawal line when a pressure in the reserve tank risesabove a predetermined maximum pressure a reserve fill line incommunication with the head space of the reserve tank and a liquidwithdrawal line of the main tank.
 4. A system as in claim 1, wherein thepressure building circuit comprises a withdrawal line extendingdownwardly from cryogenic liquid stored in the main tank and a vaporizerin the withdrawal line, wherein the cryogenic liquid stored in the maintank flows into the withdrawal line via gravity.
 5. A system as in claim1, wherein the pressure building circuit comprises a flow inducer andgas return pathway connecting from the delivery line to the vapor spaceof the main tank, wherein the flow inducer causes gas to flow from thedelivery line back to the vapor space of the main tank.
 6. A system asin claim 5, further comprising at least one flow inducer selection valveupstream of the flow inducer, wherein the selection valve canselectively flow fuel from either the delivery line of the main tank orthe vapor space of the reserve tank through the flow inducer to the headspace of the main tank.
 7. A system as in claim 1, further comprising atleast one fuel selection valve in the fuel delivery line, wherein thefuel selection valve selectively flows fuel from either the main tank orthe reserve tank to the use device through the fuel delivery line.
 8. Asystem as in claim 7, further comprising a controller that switches thevalve to a first state that directs fuel from the main tank through thefuel delivery line to the use device, and a second state that thatdirects fuel from the reserve tank through the fuel delivery line to theuse device.
 9. A system as in claim 8, wherein the controllerautomatically switches the valve between the first and second stateswithout input from a human.
 10. A system as in claim 1, wherein at leastone of the main tank and the reserve tank is formed or an outer tank andan inner tank inside the outer tank with a vacuum space between theouter tank an inner tank.
 11. A system as in claim 4, wherein thewithdrawal line has a first end inside the main tank and a second endpositioned vertically below the main tank.
 12. A system as in claim 4,further comprising a vaporizer in the withdrawal line.
 13. A system asin claim 2, wherein a biasing relief valve is included in the mainliquid withdrawal line cause the main economizer circuit to be a path ofleast resistance out of the main tank when a regulator is open.
 14. Asystem as in claim 13, wherein a small orifice is located in parallelwith the relief valve to allow back flow to the main tank duringtransient periods of high to low use.
 15. A system as in claim 14wherein a biasing relief valve is included in the reserve liquidwithdrawal line cause the reserve economizer circuit to be a path ofleast resistance out of the reserve tank when a regulator is open.
 16. Asystem as in claim 15, wherein a small orifice is located in parallelwith the relief valve in the reserve liquid withdrawal line to allowback flow to the reserve tank during transient periods of high to lowuse.
 17. A method of refilling the reserve tank with saturated liquid asin the system of claim 6 wherein the flow inducer selection valve can beset to take fluid from the vapor space of the reserve tank, therebycausing cryogenic liquid to flow from the main tank through a liquidwithdrawal line through the reserve tank fill line to the reserve tankwhile either tank is connected to the use device or while the use deviceis not using fuel.
 18. A method of refilling the reserve tank withsaturated liquid as in the system of claim 4, wherein the economizercircuit of the main tank is set to a higher pressure set point than theeconomizer circuit of the reserve tank, thereby causing cryogenic liquidto flow from the main tank while the reserve tank is connected to theuse device.
 19. A method of refilling the reserve tank with saturatedliquid as in the system of claim 5, wherein the economizer circuit ofthe main tank is set to a higher pressure set point than the economizercircuit of the reserve tank, thereby causing cryogenic liquid to flowfrom the main tank while the reserve tank is connected to the usedevice.